1. Field of the Invention
The invention relates to assembled hollow shafts, comprising an inner shaft tube with external functional elements, joined by means of radial expansion in given sections in the axial direction, whereby the inner shaft tube is deformed plastically in the expansion sections and the functional elements are only deformed resiliently in the expansion sections and the expansion sections lie between the functional elements, whereby the functional elements are combined in part into multiple functional elements. The invention also relates to processes for producing shafts of this type and for producing multiple functional elements to be used in manufacturing assembled hollow shafts.
2. Description of the Prior Art
Given the growing importance of multiple valve technology in the field of drive and control shafts (especially cam shafts) for internal combustion engines, the problem of constructing shafts that have many closely adjacent elements, such as cams and other functional parts as well as slide bearings and axial stops, arises ever more frequently. This problem poses increasing difficulties when conventional methods are used. Another problem, especially in large-diameter shafts, is that of weight, which increases quadratically.
Interesting approaches to this set of problems have been made, particularly in the field of assembled hollow cam shafts. Although the problem of cam spacing with decreasing weight can be overcome, other difficulties then arise with respect to decreasing torsional stiffness. Furthermore, the number of functional elements that must be applied to and positioned precisely on each shaft becomes very large. In the case of truck shafts, especially for diesel engines, this problem is accompanied by another difficulty, namely, the necessity of keeping the wall of the hollow shaft relatively thick, even in the single-layered areas between functional elements, for the sake of the required torsional stiffness. The advantage of reduced weight can therefore not be achieved to the desired extent.
Finally, lengthy preparation time is required prior to assembly, especially in the case of long shafts, due to the slow introduction of high-pressure probes into the hollow shaft, for example. This lengthy preparation time reduces the productivity of expensive capital resources.
A reduction in at least some of the aforementioned problems in the production of assembled hollow shafts can be attained by using multiple functional elements, e.g., multiple cams. For example, it has been proposed to produce multiple cams from tube profiles by means of twisting, or from sheet metal blanks, which are suitably shaped, formed into annular bodies and welded.
The first of these proposals, however, is limited to uniform cam profiles. Furthermore, the cams do not possess great stiffness against external pressure, e.g., follower pressure. Moreover, both proposals have very sharp limitations with respect to the spreading or the varied angular pitch of cam tips around the circumference. This limitation can be overcome in the second proposal only by using an expensive process variant.
Generic hollow shafts are known from EP-A-292 795. Double cam elements are described therein, in which an expansion section is arranged between the two external cam sections. The reason for this structure is that the cam sections of the one-piece double cam are subsequently hardened and, due to embrittlement, are not resiliently deformable to the desired extent, so that only the non-hardened middle sections are expanded. These double cams have the disadvantage, however, that the cam sections must be clearly spaced from one another, as a result of which the design of shafts with many closely adjacent functional elements is made more difficult or prevented. Moreover, the combination is limited to two elements with the same function or load.